The TwentyNineteen theme has a minimal feature almost just a skeleton, it's only normal for it to load near zero second. And as more features are added, it will become more complex which would require most of the resources and loading time hence you can't actually compare a fully different theme to an almost empty theme. And you have only shown the percentage load of 77% which is normal, it's even normal to get 100% of it because that only means you're able to use 100% of resources alotted to your hosting plan. Example, there is no point of having a 1GB plan but you're only restricted to 512mb.
And, you're only monitoring it with Query monitor which only monitors the database requests bypassing the caches, it doesn't measure the actual loading of your entire site including what's already optimized.
But again, I'm not saying there is nothing wrong because even with the TwentyNineteen, it loads half a second on my installation.
I did some checking at the front and it loads about 1.88 seconds. Then I checked the admin (just the admin dashboard, plugins, and other admin pages) and it loads about 10 to 15 seconds, it's the areas where the builder features are inactive but still loads that longer. Please note that the builder resources and features are only running once the builder is loaded so it shouldn't affect any area of the admin. All database queries are handled by Wordpress and the theme only uses the functions and features provided by it. Any query optimization should be done between your Wordpress and host configuration, please check this https://css-tricks.com/finding-and-fixing-slow-wordpress-database-queries/.
And this is a screenshot of the query monitor for slow query in the dashboard
And itself belongs to Wordpress transient's query. And then below is for the plugins page
And they are still related to Wordpress transients and WP Rockets table.
And this for pages section
And still transient related issue and it makes the request slower, perhaps, Wordpress transient has issues with your hosting environment. The more the plugins, theme, and or active features, the more it has hard time handling the transients (internal cache of Wordpress).
Or do you mean the builder should load less than 2 seconds? Because that's impossible depending on the amount of the content it needs to load. And it's only normal for the builder to load around than 3-10seconds, or more.